Threads are used on a wide array of mechanical components, piping, and conduit for engaging components together and/or to provide a sealing connection between components. Numerous thread sizes and thread configurations are known, such as tapered threads and non-tapered or “straight” threads. Within each class, a variety of different thread forms have been developed and used depending upon the application, type of work piece, customs of the locale, and preferences of the user.
Devices for forming threads on pipe ends are well known in the art. Such devices use one or more dies that form a helical thread extending from one region of the pipe to another region. The die is orbited about the axis of the pipe and/or the pipe is rotated while the die is engaged with a select region of the pipe to form the thread.
When assembling piping systems or when forming custom piping layouts, sections of pipe are typically cut and threaded at a construction or assembly site. As a result, portable or semi-portable pipe threading devices have been developed which can be used at the job site to prepare threaded pipe ends.
Presently, hand held power drive units are known which provide power to die heads during thread cutting operations on pipes. This power is provided by the power drive with angular velocity and torque dependent upon the type of thread, dies, and pipe. In such an operation, the die head needs to be retained in an axial direction to prevent disengagement with the power drive spindle. Particularly, force must be applied to the die head in the axial direction during the initial engagement of the die head with the pipe. In a present configuration of such power drives, a spring ring is used to lock the die head, which necessitates a higher effort for installing or removing the die head in the assembly. Moreover, for locking the axial movement of the die head in such assembly, the spring ring must be snap fitted in a groove on a face gear in order to provide locking of the die head. Thus, an exceedingly high force is required to fully engage the die head in the face gear with the spring ring, thus resulting in a cumbersome and time consuming operation. Furthermore, with continued use, this spring ring loses its stiffness and locking force so that replacement may be required.
Other power drive units either use an internally threaded disc for axial locking of the die head or use a retaining ring to lock the die head. As a consequence, greater time is required for installing or removing the die head. The retaining ring is inserted behind the die head (after installation of the die head in the power drive) in an available groove. Therefore, an external device (e.g. a screw driver) is necessary for installing or removing the die head.
The following descriptions represent the state of the art relating to die head retaining mechanisms in pipe cutting or threading machines.
CN 101704141 discloses an electric pipe cutting threading machine, aiming at overcoming the problems of narrow application range and low machining accuracy of common threading machines. The electric pipe cutting threading machine comprises an automatic cutter-withdrawal device, a die head, a scraper and a cutting knife. The machine is characterized in that the die head comprises a baffle, a locking screw, a release lever, a transmission screw pressure spring, a transmission screw, a fastening card, a curve locking disk which is arranged between a curve disk and a salver, and a locking hole which is cut on the curve disk. Further, a moon-groove is arranged on a die-disk, and the transmission screw pressure spring and the transmission screw are arranged in this moon-groove. A transmission hole is arranged on the curve locking disk, which is penetrated by the transmission screw. The baffle is shaped in an ‘L’ shape which is reversed vertically and articulated on the curve locking disk. The curve locking disk is provided with a blocking handle and a limiting lug. The release lever is articulated on the die-disk. The automatic cutter-withdrawal device comprises a sine block, a guiding rod, a left pressure spring and a right pressure spring, wherein the sine block is sheathed on the guiding rod and the left pressure spring and the right pressure spring are respectively fixed at two ends of the guiding rod.
CN 201644960 discloses a self-opening die head used in an electric tube-cut wire-sleeving machine. The machine comprises a tray, a die with raised line grooves, a die tray with die grooves and a curve tray with arc raised lines and is characterized by also comprising a baffle, a locking screw, an unlocking handle, a transmission bolt pressure spring, a transmission bolt, a stopping tag and a curve locking disc with an arc adjusting groove. The curve locking disc is mounted between the tray and the curve tray which is internally provided with a locking hole. The locking screw penetrates through the locking hole and the arc adjusting groove. The die tray is provided with moon grooves. The transmission bolt pressure spring and the transmission bolt are mounted in the moon grooves. The curve locking disc is provided with a transmission hole in which the transmission bolt penetrates. The baffle is articulated on the curve locking disc which is provided with a baffle handle and a stopping lug boss. And the unlocking handle is articulated with the periphery of the die tray.
U.S. Pat. No. 2,958,877 discloses a self-opening die head comprising a skeleton or frame having a hollow elongated shank, chasers mounted on the skeleton for reciprocal movement into and out of a work-engaging position, and a chaser-operating member for moving the chasers into a work-engaging position. The combination comprises a ring shaped latch-unit positioned around the shank and having a latching portion movable transversely outwardly with respect to the longitudinal axis of the shank into a latching position with the chaser-operating member in order to releasably hold the member in its chaser-closing position. The combination also comprises a spring means resiliently urging the latch-unit into the latching position. The combination also comprises tripping means mounted within the shank of the skeleton for releasing the chaser-operating member. The tripping means has a trip member movable axially of the shank and located with one end in position for engagement with the work. The tripping means also has camming means engaging the inner surface of the latch-unit at a point diametrically opposite the latching portion and operable upon axial movement of the trip member to cam the latch-unit against the urging of the spring means and thereby move the latching portion out of the latching position. The latch-unit comprises a pair of complementary segments, a first of the segments comprising the latching portion, and the second of the segments being interlocked with the first so as to draw the first segment inwardly to an unlatching position upon actuation of the trip member.
U.S. Pat. No. 2,739,322 discloses a thread cutting die head, in which a body member is provided with a relatively fixed abutment, and an axially shiftable chaser holder closing ring is mounted on the body member and resiliently biased toward the abutment in axial alignment therewith. The closing ring has first and second annular radial surfaces offset axially and facing the abutment. A locking ring extends around the axis of the die head and is positioned between the closing ring and the abutment and has annular front and rear faces. Means are also disclosed to bodily displace the locking ring laterally of the die head between a first position to dispose the front face thereof in engagement with the first surface on the closing ring and a second position to dispose the front face thereof in engagement with the second surface of the closing ring. The rear face of the locking ring is engaged with the abutment in both positions whereby the locking ring is fixed against axial movement. The respective areas of engagement between the locking ring and the first and second surfaces and between the locking ring and the abutment are disposed at least in any three selected quadrants about the axis of the head.
Although prior art assemblies and techniques are somewhat satisfactory, a need remains for an improved mechanism and strategy for retaining a die head in a thread cutting machine.